Diffuser for a gas turbine

ABSTRACT

A diffuser for a gas turbine includes an inlet adapted for coupling to the gas turbine. The diffuser also includes at least one outlet located proximate a diffuser end, wherein the diffuser end is located downstream of the inlet. The diffuser further includes an outer wall and an inner barrel that extends substantially to the diffuser end.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to turbines and, inparticular, to diffusers for use with gas turbines and steam turbines.

Typical gas turbines include a diffuser cone, or diffuser, coupled tothe last stage bucket of the rotor. The diffuser serves, generally, toincrease static pressure of the exhaust gas by decreasing the kineticenergy of the exhaust gas. Generally, this may be achieved by increasingthe cross-sectional area of the diffuser in the direction of exhaust gasflow.

Often, gas turbines are not operated at full load, but are designed forefficiency under such a full load. Therefore, part load performanceefficiency is sacrificed, based on the full load design. Suchinefficiencies are due, at least in part, to flow separation on thediffuser inner barrel, leading to tip strong flow profiles. Otherfactors, such as operation of the last stage of the turbine, mayinfluence the flow profile. Additionally, flow passing over a centerbody of the diffuser generates large vortices that result in yet furthersystem inefficiency.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a diffuser for a gas turbineincludes an inlet adapted for coupling to the gas turbine. The diffuseralso includes at least one outlet located proximate a diffuser end,wherein the diffuser end is located downstream of the inlet. Thediffuser further includes an outer wall and an inner barrel extendingsubstantially to the diffuser end.

According to another aspect of the invention, an exhaust gas diffuserincludes an inlet and an outlet. The exhaust gas diffuser also includesan inner barrel extending from substantially the inlet to substantiallythe outlet. The diffuser further includes an outer wall radially spacedapart from the inner barrel, wherein the outer wall and the inner barreldefine a varying radius along a length of the diffuser between the inletand the outlet.

According to yet another aspect of the invention, a gas turbine includesa turbine casing that surrounds a portion of the gas turbine. The gasturbine also includes an exhaust gas diffuser coupled to the turbinecasing. The diffuser includes an inlet adapted for coupling to the gasturbine, an outer wall, an inner barrel and a diffuser end downstreamfrom the inlet, the inner barrel extending substantially to the diffuserend.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a side, cross-sectional view of a diffuser according to oneaspect of the invention;

FIG. 2 illustrates a flow profile associated with the diffuserillustrated in FIG. 1;

FIG. 3 illustrates a diffuser flow profile exhibiting flow separation;and

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one aspect of a diffuser 200 according to oneembodiment of the present invention. In operation, exhaust gas from thegas turbine flows through the diffuser 200 in the direction shown byarrow A. In this description, an object is “downstream” of anotherobject or location if it is displaced from it in the direction of arrowA and is “upstream” if it is displaced from it in a direction oppositeof arrow A.

The diffuser 200 includes an inner barrel 202 that includes an innerwall 204 that forms an inner chamber 208 through which a portion of arotor may pass. The diffuser 200 includes an inlet 211 located proximatea diffuser entry end 210 and an outlet 220 located proximate a diffuserexit end 222. The inlet 211 may be coupled to a turbine, while theoutlet 220 may be coupled to an adjacent object, such as a silencer. Thediffuser also includes an outer wall 206 radially spaced from the innerwall 204 of the inner barrel 202. The area between the inner wall 204and the outer wall 206 allows fluid or gas to flow downstreamtherethrough from the inlet 211 to the outlet 220 of the diffuser 200.

The diffuser 200 may also include one or more struts 216 formed betweenthe inner wall 204 and the outer wall 206. The strut 216 serves to holdthe inner wall 204 and the outer wall 206 in a fixed relationship to oneanother, as well as providing bearing support. The number of struts 216is variable and commonly ranges from about four to about ten.

The inner wall 204 of the inner barrel 202 extends from the inlet 211,or diffuser entry end 210, to the outlet 220, or diffuser exit end 222.The inner barrel 202, and hence the inner wall 204, includes a first end224 located proximate the inlet 211 and a second end 226 locatedproximate the outlet 220 and may take on numerous longitudinal contoursas the inner barrel 202 extends from the first end 224 to the second end226. The inner barrel 202 may slightly curve continuously from the firstend 224 to the second end 226, may curve slightly for only portionsbetween the first end 224 and the second end 226, may extend in asubstantially straight direction, or may comprise segmented portions,where the overall longitudinal direction of the inner barrel 202comprises any combination of the curvilinear paths described above.Irrespective of the shape of the inner barrel 202, and more particularlythe inner wall 204, the inner barrel 202 and inner wall 204 extend tothe diffuser outlet 220 or diffuser exit 222.

The outer wall 206 includes a first portion 230 that extends from theinlet 211, or diffuser entry end 210, in a substantially downstreamdirection, as well as in a direction away from the inner wall 204. Thesloping curvilinear direction of first portion 230 of the outer wall 206terminates at an outer radius location 232. The outer wall 206 alsoincludes a second portion 234 that extends from the outer radiuslocation 232 in a substantially downstream direction to the outlet 220,or diffuser exit end 222. The first portion 230 of the outer wall 206angles away from the inner wall 204 more substantially than the secondportion of the outer wall 206, with the outer radius location 232 beinglocated further upstream than a longitudinal midpoint 236 of the innerbarrel 202. The portion of the inner barrel 202 located upstream of thelongitudinal midpoint 236 is an inlet portion 238, while the portion ofthe inner barrel located downstream of the longitudinal midpoint 236 isan outlet portion 240. Therefore, the outer wall 206 is pushed to anouter radius further upstream than conventional diffuser outer wallconstructions.

FIG. 2 shows a flow path profile in diffuser 200 shown in FIG. 1. As canbe seen, the flow profile for the diffuser 200 of FIG. 1 is strongthroughout the entire radial area of the diffuser 200, even along theinner wall 204. The diffuser 200 reduces flow separation, therebyimproving diffuser performance over a diffuser flow profile exhibitingflow separation, as shown in FIG. 3.

In addition to reducing flow separation by employing the above-describeddiffuser 200 structure, the introduction of secondary air flow may beinjected into the diffuser 200. Such a secondary air flow into thediffuser 200 and thereby a main diffuser flow alters overall flow byenergizing a shear layer that is formed between the main flow and theinner wall 204 and/or outer wall 206, causing a delay of the flowseparation itself The main flow widens and a larger static pressurerecovery is achieved.

Various approaches to achieve introduction of the secondary air flow arecontemplated and one such approach is by installing a flow manipulationdevice, such as a pump, within the inner barrel 202. The inner wall 204of the inner barrel 202 includes one or more actuator openings and oneor more suction openings that are located downstream of the one or moreactuator openings. The suction opening allows common weak flow thatpasses directly over the inner wall 204 to enter the inner barrel 202and pass through the flow manipulating device with sufficient force toexit the actuating opening in a manner that manipulates the flow profileof the diffuser 200. The manipulation of flow reduces flow separation,thereby increasing diffusion area.

Advantageously, diffuser 200 flow path is controlled by focusing thediffusion gradient near the region of high velocity and radiallyredistributing the flow. To reduce flow separation within the diffuser200, particularly during part load performance of the overall system,the inner barrel 202 extends to the relative outlet 220 of the diffuser200. Additionally, an outer wall 206 of the diffuser 200 extendsradially away from the inner barrel 202 at a rapid rate, startingupstream at the relative inlet 211 of the diffuser 200. The result is areduction in loss producing vortices associated with wake and asignificant improvement in diffuser performance and thereby system heatrate gain. While the invention has been described in detail inconnection with only a limited number of embodiments, it should bereadily understood that the invention is not limited to such disclosedembodiments. Rather, the invention can be modified to incorporate anynumber of variations, alterations, substitutions or equivalentarrangements not heretofore described, but which are commensurate withthe spirit and scope of the invention. Additionally, while variousembodiments of the invention have been described, it is to be understoodthat aspects of the invention may include only some of the describedembodiments. Accordingly, the invention is not to be seen as limited bythe foregoing description, but is only limited by the scope of theappended claims.

1. A diffuser for a gas turbine comprising: an inlet adapted forcoupling to the gas turbine; at least one outlet located proximate adiffuser end, wherein the diffuser end is located downstream of theinlet; an outer wall; and an inner barrel extending substantially to thediffuser end.
 2. The diffuser of claim 1, wherein the outer wall and theinner barrel define a varying radius along a length of the diffuserbetween the inlet and the outlet.
 3. The diffuser of claim 2, whereinthe varying radius defined by the outer wall and the inner barrel isgreater at the outlet than at the inlet.
 4. The diffuser of claim 2,wherein the varying radius defined by the outer wall and the innerbarrel includes an outer radius location.
 5. The diffuser of claim 4,further comprising a midpoint located relatively halfway between theinlet and the outlet, an inlet portion defined by the inlet and themidpoint, and an outlet portion defined by the midpoint and the outlet,wherein the outer radius location is proximate the inlet portion.
 6. Thediffuser of claim 1, in combination with an axial-flow turbine.
 7. Thediffuser of claim 1, wherein the outlet is adapted for coupling to anadjacent object.
 8. An exhaust gas diffuser comprising: an inlet; anoutlet; an inner barrel extending from substantially the inlet tosubstantially the outlet; and an outer wall radially spaced apart fromthe inner barrel, wherein the outer wall and the inner barrel define avarying radius along a length of the diffuser between the inlet and theoutlet.
 9. The diffuser of claim 8, wherein the varying radius definedby the outer wall and the inner barrel is greater at the outlet than atthe inlet.
 10. The diffuser of claim 8, wherein the varying radiusdefined by the outer wall and the inner barrel includes an outer radiuslocation.
 11. The diffuser of claim 10, further comprising a midpointlocated relatively halfway between the inlet and the outlet, an inletportion defined by the inlet and the midpoint, and an outlet portiondefined by the midpoint and the outlet, wherein the outer radiuslocation is proximate the inlet portion.
 12. The exhaust gas diffuser ofclaim 8, in combination with an axial-flow gas turbine.
 13. The exhaustgas diffuser of claim 12, wherein the inlet is adapted for coupling tothe axial-flow gas turbine.
 14. The exhaust gas diffuser of claim 12,wherein the outlet is adapted for coupling to an adjacent object.
 15. Agas turbine comprising: a turbine casing that surrounds a portion of thegas turbine; and an exhaust gas diffuser coupled to the turbine casing,the diffuser including: an inlet adapted for coupling to the gasturbine, an outer wall, an inner barrel and a diffuser end downstreamfrom the inlet, the inner barrel extending substantially to the diffuserend.
 16. The gas turbine of claim 15, wherein the exhaust gas diffuserfurther comprises an outlet located proximate the diffuser end.
 17. Thegas turbine of claim 16, wherein the outer wall and the inner barreldefine a varying radius along a length of the diffuser between the inletand the outlet.
 18. The gas turbine of claim 17, wherein the varyingradius defined by the outer wall and the inner barrel is greater at theoutlet than at the inlet.
 19. The gas turbine of claim 17, wherein thevarying radius defined by the outer wall and the inner barrel includesan outer radius location.
 20. The gas turbine of claim 19, wherein theexhaust gas diffuser further comprises a midpoint located relativelyhalfway between the inlet and the outlet, an inlet portion defined bythe inlet and the midpoint, and an outlet portion defined by themidpoint and the outlet, wherein the outer radius location is proximatethe inlet portion.